Various types of spinal column disorders are known and include scoliosis (abnormal lateral curvature of the spine), kyphosis (abnormal backward curvature of the spine), excess lordosis (abnormal forward curvature of the spine), spondylolisthesis (forward displacement of a lumbar vertebra) and other disorders, such as ruptured or slipped discs, broken or fractured vertebrae and the like. Patients who suffer from such conditions often experience extreme and debilitating pain. A technique known as spinal fixation uses surgical implants which mechanically immobilize areas of the spine assisting the eventual fusion of the treated vertebrae. Such techniques have been used effectively to treat the above-described conditions and, in most cases, to give the patient relief from pain.
One particular technique for spinal fixation includes the immobilization of the spine by the use of a pair of spine rods that run parallel to the spine on the left and right sides of the spinous process. According to the technique, bone screws are applied in the pedicles of the appropriate vertebrae or to the sacrum, to act as the anchor points for the spine rods. The bone screws are generally placed two per vertebra, one at each pedicle on either side of the spinous process. Clamp assemblies join the spine rods to the screws. The spine rods are generally custom-bent to achieve the desired curvature of the spinal column. Examples of such spinal fixation devices can be found in U.S. Pat. Nos. 4,653,481 and 5,030,220, which are incorporated herein by reference. According to another technique, rather than using bone screws, lamina hooks can be fastened to a spine rod to connect one or more rods to a vertebra for distraction or compression.
It has been found that when a pair of spine rods are fastened in parallel on either side of the spinous process, the assembly can be significantly strengthened by using at least one additional stiffening member known as a transverse connector to horizontally connect the pair of spine rods. A number of different transverse connectors are known. Ideally such transverse connectors should provide strength and control torsion.
Installation of a spinal fixation device entails a lengthy and complicated surgical procedure. Therefore, any simplification of the assembly procedure of a spinal fixation device will tend to reduce the complications associated with the procedure. For this reason, a transverse connector should be simple in installation.